Alloys with the composition (R E_{h}(\mathrm{Fe}, \mathrm{Co}){13} X(R E=\mathrm{La}, \mathrm{Pr}, \mathrm{Nd}, \mathrm{Sm} ; X=\mathrm{As}, \mathrm{In}, \mathrm{Sn}, \mathrm{Sb}, \mathrm{Tl}, \mathrm{Pb}, \mathrm{Bi})) have been synthesized by the arc melting technique, followed by annealing at (873-1273 \mathrm{~K}) for up to (170 \mathrm{hr}) in evacuated silica capsules. From room temperature X-ray powder diffraction analysis the alloys were found to crystallize with the ordered (\mathrm{La}{6} \mathrm{Co}{11} \mathrm{Ga}{3}), i.e., the (\mathrm{Nd}{6} \mathrm{Fe}{13} \mathrm{Si}) type of structure. Precise atom parameters and interatomic distances have been derived from a single crystal X-ray refinement of (\mathrm{Pr}{6} \mathrm{Fe}{13} \mathrm{~Pb}). The (\mathrm{La}{6} \mathrm{Co}{13} X) compounds exhibit ferromagnetism with a saturation moment of (\mu_{\mathrm{S}} \sim 1 \mu_{\mathrm{R}} /) cobalt atom. From the magnetic behavior of the iron-containing samples antiferromagnetic compling of : t least Iwo magnetic sublatlices is conctuded to be present because of the strongly reduced magnetizalion values. While the "Fe Mössbauer spectra are essentially unaffected by the specific element (X). a modified shape of the spectra is obscrved if the rare earth element is changed. In the case of (R E=\mathrm{Nd}) the spectra indicate an easy (c)-axis of magnetization in the whole range between room and liquid helium temperalure; in the case of (R E=\operatorname{Pr}) a spin reorientation is anticipated. (o) 1993 Academic Press. Inc.